Handle STATUS command without backends

include/MySQL_Session.h

@@ -133,6 +133,7 @@ class MySQL_Session
 
 	void return_proxysql_internal(PtrSize_t *);
 	bool handler_special_queries(PtrSize_t *);
+	bool handler_special_queries_STATUS(PtrSize_t *);
 	/**
 	 * @brief Handles 'COMMIT|ROLLBACK' commands.
 	 * @details Forwarding the packet is required when there are active transactions. Since we are limited to

include/sqlite3db.h

@@ -155,6 +155,7 @@ class SQLite3_result {
 	void add_column_definition(int a, const char *b);
 	int add_row(sqlite3_stmt *stmt, bool skip=false);
 	int add_row(char **_fields);
+	int add_row(const char **_fields) { return add_row((char **)_fields); }
 	int add_row(SQLite3_row *old_row);
 	int add_row(const char* _field, ...);
 	SQLite3_result(sqlite3_stmt *stmt);

lib/MySQL_Session.cpp

@@ -25,7 +25,10 @@
 
 #define SELECT_VERSION_COMMENT "select @@version_comment limit 1"
 #define SELECT_VERSION_COMMENT_LEN 32
-
+#define SELECT_DB_USER "select DATABASE(), USER() limit 1"
+#define SELECT_DB_USER_LEN 33
+#define SELECT_CHARSET_STATUS "select @@character_set_client, @@character_set_connection, @@character_set_server, @@character_set_database limit 1"
+#define SELECT_CHARSET_STATUS_LEN 115
 #define PROXYSQL_VERSION_COMMENT "\x01\x00\x00\x01\x01\x27\x00\x00\x02\x03\x64\x65\x66\x00\x00\x00\x11\x40\x40\x76\x65\x72\x73\x69\x6f\x6e\x5f\x63\x6f\x6d\x6d\x65\x6e\x74\x00\x0c\x21\x00\x18\x00\x00\x00\xfd\x00\x00\x1f\x00\x00\x05\x00\x00\x03\xfe\x00\x00\x02\x00\x0b\x00\x00\x04\x0a(ProxySQL)\x05\x00\x00\x05\xfe\x00\x00\x02\x00"
 #define PROXYSQL_VERSION_COMMENT_LEN 81
 
@@ -1320,9 +1323,83 @@ void MySQL_Session::return_proxysql_internal(PtrSize_t *pkt) {
 	l_free(pkt->size,pkt->ptr);
 }
 
+/**
+ * @brief Handles special queries executed by the STATUS command in mysql cli .
+ *   Specifically:
+ *   "select DATABASE(), USER() limit 1"
+ *   "select @@character_set_client, @@character_set_connection, @@character_set_server, @@character_set_database limit 1"
+ *   See Github issues 4396 and 4426
+ *
+ * @param PtrSize_t The packet from the client
+ *
+ * @return True if the queries are handled
+ */
+bool MySQL_Session::handler_special_queries_STATUS(PtrSize_t *pkt) {
+	if (pkt->size == (SELECT_DB_USER_LEN+5)) {
+		if (strncasecmp(SELECT_DB_USER,(char *)pkt->ptr+5, SELECT_DB_USER_LEN)==0) {
+			SQLite3_result *resultset = new SQLite3_result(2);
+			resultset->add_column_definition(SQLITE_TEXT,"DATABASE()");
+			resultset->add_column_definition(SQLITE_TEXT,"USER()");
+			char *pta[2];
+			pta[0] = client_myds->myconn->userinfo->username;
+			pta[1] = client_myds->myconn->userinfo->schemaname;
+			resultset->add_row(pta);
+			bool deprecate_eof_active = client_myds->myconn->options.client_flag & CLIENT_DEPRECATE_EOF;
+			SQLite3_to_MySQL(resultset, NULL, 0, &client_myds->myprot, false, deprecate_eof_active);
+			delete resultset;
+			l_free(pkt->size,pkt->ptr);
+			return true;
+		}
+	}
+	if (pkt->size == (SELECT_CHARSET_STATUS_LEN+5)) {
+		if (strncasecmp(SELECT_CHARSET_STATUS,(char *)pkt->ptr+5, SELECT_CHARSET_STATUS_LEN)==0) {
+			SQLite3_result *resultset = new SQLite3_result(4);
+			resultset->add_column_definition(SQLITE_TEXT,"@@character_set_client");
+			resultset->add_column_definition(SQLITE_TEXT,"@@character_set_connection");
+			resultset->add_column_definition(SQLITE_TEXT,"@@character_set_server");
+			resultset->add_column_definition(SQLITE_TEXT,"@@character_set_database");
+
+			string vals[4];
+			json j = {};
+			MySQL_Connection *conn = client_myds->myconn;
+			// here we do a bit back and forth to and from JSON to reuse existing code instead of writing new code.
+			// This is not great for performance, but this query is rarely executed.
+			conn->variables[SQL_CHARACTER_SET_CLIENT].fill_client_internal_session(j, SQL_CHARACTER_SET_CLIENT);
+			conn->variables[SQL_CHARACTER_SET_CONNECTION].fill_client_internal_session(j, SQL_CHARACTER_SET_CONNECTION);
+			conn->variables[SQL_CHARACTER_SET_DATABASE].fill_client_internal_session(j, SQL_CHARACTER_SET_DATABASE);
+
+			vals[0] = j["conn"][mysql_tracked_variables[SQL_CHARACTER_SET_CLIENT].internal_variable_name];
+			vals[1] = j["conn"][mysql_tracked_variables[SQL_CHARACTER_SET_CONNECTION].internal_variable_name];
+			vals[2] = string(mysql_thread___default_variables[SQL_CHARACTER_SET]);
+			vals[3] = j["conn"][mysql_tracked_variables[SQL_CHARACTER_SET_DATABASE].internal_variable_name];
+
+			const char *pta[4];
+			for (int i=0; i<4; i++) {
+				pta[i] = vals[i].c_str();
+			}
+			resultset->add_row(pta);
+			bool deprecate_eof_active = client_myds->myconn->options.client_flag & CLIENT_DEPRECATE_EOF;
+			SQLite3_to_MySQL(resultset, NULL, 0, &client_myds->myprot, false, deprecate_eof_active);
+			delete resultset;
+			l_free(pkt->size,pkt->ptr);
+			return true;
+		}
+	}
+	return false;
+}
+
 bool MySQL_Session::handler_special_queries(PtrSize_t *pkt) {
 	bool deprecate_eof_active = client_myds->myconn->options.client_flag & CLIENT_DEPRECATE_EOF;
 
+	if (
+		(pkt->size == (SELECT_DB_USER_LEN+5))
+		||
+		(pkt->size == (SELECT_CHARSET_STATUS_LEN+5))
+	) {
+		if (handler_special_queries_STATUS(pkt) == true) {
+			return true;
+		}
+	}
 	if (pkt->size>(5+18) && strncasecmp((char *)"PROXYSQL INTERNAL ",(char *)pkt->ptr+5,18)==0) {
 		return_proxysql_internal(pkt);
 		return true;